This invention relates to the field of fluid particle contact and to an apparatus for contacting fluids and particles. The invention further relates to fluid conduits which form the outer retaining wall for an annular particulate bed used in a radial flow system mounted in a cylindrical vessel. In such systems a fluid typically is directed radially inwardly or outwardly into or out of the particulate bed through openings in the inner surfaces of a plurality of outer, vertically arranged conduit members or through openings in a cylindrical screen basket member which has a smaller diameter than the inner wall of the vessel. The fluid passes through openings in a vertically arranged center pipe which forms the inner retaining wall for the annular particulate bed. The invention more particularly relates to fluid conduits having at least one tapered side relative to at least one reactor wall.
A wide variety of processes use radial flow reactors to provide for contact between a fluid and a solid. The solid usually comprises a catalytic material on which the fluid reacts to form a product. The processes cover a range of processes, including hydrocarbon conversion, gas treatment, and adsorption for separation.
Radial flow reactors are constructed such that the reactor has an annular structure and there are annular distribution and collection devices. The devices for distribution and collection incorporate some type of screened surface. The screened surface is for holding catalyst beds in place and for aiding in the distribution of pressure over the surface of the reactor to facilitate radial flow through the reactor bed. The screen can be a mesh, either wire or other material, profile wire, or a punched plate. For a moving bed, the screen or mesh provides a barrier to prevent the loss of solid catalyst particles while allowing fluid to flow through the bed. Solid catalyst particles are added at the top, and flow through the apparatus and removed at the bottom, while passing through a screened-in enclosure that permits the flow of fluid over the catalyst. The screen is preferably constructed of a non-reactive material.
The screens or meshes used to hold the catalyst particles within a bed are sized to have apertures sufficiently small that the particles cannot pass through. The vessel typically is a reactor which contains a bed of particulate material such as catalyst, absorbent, resins or activated carbon. The fluid which passes through the particulate bed in a radial direction is usually a gas, but it could also be a liquid or a liquid/gas mixture. In prior art systems, the outer wall support for the annular particulate bed is often a ring of individual scallops members which have convex inner surfaces and outer surfaces which conform to the wall of the vessel. The scallops members can be formed from metal plates which contain perforations smaller in diameter than the size of the particulate material. They can also be formed with their convex inner surface comprising a screen element having a plurality of closely spaced wires welded to support rods. Such scallops are often sized so they can be installed or replaced when required by lifting them through an opening in the top of the vessel. Another type of prior art system includes a cylindrical screen basket member which is spaced inwardly from the outer wall of the vessel. Such a cylindrically shaped screen basket member cooperates with an inner screen pipe member to cause the particulate bed positioned between such inner and outer members to have a uniform thickness. However, the systems is quite expensive since the large diameter screen cannot be installed or removed through a small upper opening in the vessel, as can the scallops type screen. In other embodiments, instead of individual scallops, the same function may be served by a screen that is mounted to cover the same area as the ring of individual scallops.
Examples of prior art systems which have scallops members around the inside surface of the outer vessel wall include Hansen, Jr. U.S. Pat. No. 3,167,399 and Koves et al U.S. Pat. No. 5,209,908. Farnham U.S. Pat. No. 4,374,094 shows vertical screen segments surrounding an annular catalyst bed which are spaced from the side wall of the vessel. Schuurman U.S. Pat. No. 4,540,547 shows a moving bed reactor wherein a ring of screen segments surrounds a centrally located catalyst bed and separates the catalyst from the outer annular chamber which receives the effluent after it passes through the screen surfaces. Nagaoka EP 0483975 A1 shows a device for holding particulate catalyst in a radial flow reactor which comprises a ring of vertically arranged containers having abutting side walls and screened inner walls, the containers being filled with catalyst and positioned between an annular outer fluid chamber and an inner cylindrical fluid chamber.
It has now been found that varying the catalyst bed depth and volume provides advantages in the operation of a reactor. This is useful in the chemical industry for maximum utilization of reactor vessel volumes, and the overall catalyst content in the reactor can be increased by more than 20% through the use of the present invention. A further advantage is that catalyst may be more efficiently utilized. Since the catalyst is deactivating via coke buildup as it falls through the reacting space. Having additional residence time in the lower regions of the reactor is favorable for process chemistries that involve deactivating catalysts. The present invention uses hydraulic balancing to achieve a significant increase in bed depth within constraints on cross-flow inner screen pinning design and overall reactor pressure drop. The path length found on the bottom of the vessel can even be increased by more than 33% in one case.
Reforming scallops sizing (depth) is typically governed by the riser entrance component to achieve acceptable pressure drop for feed distribution and minimize overall system pressure drop. This results in a significant volume for the overall piece of equipment.